It's just not going to happen and it's not a good business movie anyway. No publisher is going to give a game away for free just so PS3 owners can feel better about the PS4's lack of backwards compatibility.
Sony needs everyone to switch to the PS4. So what they really should do is shut down the PS3, move all unreleased games over to PS4 exclusives and force everyone to either upgrade to PS4 or starve for games on PS3. Not a nice move, but the smart move.
Nobody is going to buy a PS3 game while the PS4 is out planing to play it on PS4 so packing in an extra game will do nothing but lose money. The same goes for PS4 owners, they don't want a PS3 game packed in with their PS4 game. Both will just end up pulling the second disc out and sell it. That will lose publishers money.
